In formally protesting the Air Force's decision to award a tanker contract worth about $35 billion to a team that includes the parent of rival Airbus, The Boeing Co. said the competition was "seriously flawed."

The Air Force has said that it simply picked the plane that better suited its needs.

Meanwhile, The Associated Press reported Tuesday that aides to Sen. John McCain of Arizona, the presumptive Republican presidential nominee, lobbied last year on behalf of EADS. And Bloomberg News reported that the Loeffler Group, led by Tom Loeffler, now co-chairman of McCain's campaign, received $220,000 from EADS in 2007, according to congressional lobbying records.

McCain said Tuesday that his only role in the tanker issue was to try to ensure fairness.

In its formal protest, Boeing essentially accused the Air Force of manipulating critical data to not only keep the team of Northrop Grumman and the European Aeronautic Defense and Space Co. in the game after both sides had submitted their tanker bids, but of making eleventh-hour changes that gave the bigger Airbus plane an advantage over Boeing's smaller 767.

"This is pretty serious stuff; it's not nitpicking," Richard Aboulafia of the Teal Group, an industry consulting firm, said of Boeing's allegations.

"And McNerney has gotten involved, too," Aboulafia said, referring to Boeing Chairman and Chief Executive Jim McNerney. "That says to me they would not be doing this if they didn't have something. Will it carry the day? I don't know."

Although protesting Pentagon contracts has become almost routine in recent years for some contractors, the action may have been unprecedented for Boeing, the nation's second-biggest military contractor after Lockheed Martin.

A spokesman with Boeing's corporate offices in Chicago said a company historian could not find another instance in which Boeing protested the loss of a government contract.

The GAO has 100 days to investigate and issue its findings. The tanker program will be on hold until then, but the firestorm in Congress surrounding the Air Force decision is certain to continue, if not grow.

Rep. Todd Tiahrt, a Republican from Kansas, where Boeing's 767 tanker would have been flown for installation of air-refueling and other military equipment, announced that he is drafting legislation that would block funding for the Northrop-EADS tanker.

Aboulafia, the analyst, said the disclosures about McCain's aides will fuel suspicions by some that politics played some role in the Air Force's decision to pick the Airbus plane.

"The latest developments about McCain will give people the ammunition to try and make that connection -- why was this done?" Aboulafia said.

In 2004, McCain helped block a scandal-marred tanker contract with Boeing and prodded the Pentagon in 2006 to change proposed bidding procedures opposed by Airbus.

On Tuesday, AP quoted him as saying, "I had nothing to do with the (current) contract, except to insist in writing, on several occasions, as this process went forward, that it be fair and open and transparent.

"That was my involvement in it."

Lawmakers in Congress who support Boeing are outraged that the Air Force awarded the tanker contract to European-based EADS, arguing that it means the loss of U.S. jobs and could hurt national security.

The Air Force has said it did not factor employment into the competition.

In a hearing on Capitol Hill on Tuesday, Rep. Norm Dicks, D-Wash., accused the Air Force of misleading Boeing about the size of the tanker it wanted.

"I urge you to go back and start over. You made a big mistake. You did not do this right," Dicks told Air Force Secretary Michael Wynne. "I was misled in this. Boeing was misled."

In another development, Sen. Max Baucus, D-Mont., chairman of the Senate Finance Committee, said the tanker procurement decision "raises serious questions of common sense."

Baucus said he has "serious questions about this deal from the perspective of international trade," referring to subsidies that Airbus receives from European governments.

In a teleconference with reporters and analysts, Mark McGraw, vice president of tanker programs for Boeing, was asked if politics played a role in the Air Force decision.

"We are staying out of the politics," McGraw said, but added that Boeing has been "comforted by the uproar."

The Air Force had hoped that the loser of the competition would not file a protest, which means more delays in getting new tankers to replace the more than 500 Boeing-built, Eisenhower-era KC-135s operated by the Air Force and the reserves.

"It's not helpful to the department or the war fighter," John Young, the Defense Department's undersecretary for acquisition, told reporters on Capitol Hill after Boeing filed its protest.

It was Young who gave final approval to the Air Force tanker deal with Northrop-EADS.

"There's no question the Air Force can provide an abundance of facts and analysis for the decision they made," Young said after testifying to a House Armed Services subcommittee.

He said there were "substantial capability and cost differences" that turned the competition in favor of the Northrop team.

Boeing took strong issue with that argument.

In an hourlong teleconference, in which Boeing laid out its case against the Air Force and explained why it believes the tanker competition was flawed, McGraw said the tanker competition started out as fair but did not end up that way.

In a later statement, Boeing said the process was "replete with irregularities."

"As the requirements were changed to accommodate the bigger, less capable Airbus plane, evaluators arbitrarily discounted the significant strengths of the KC-767, compromising on operational capabilities," McGraw said in the written statement.

McGraw told reporters that the Northrop-EADS team pressured the Air Force to "continuously make changes so their tanker could compete."

Northrop said the competition was one of the most transparent and rigorous ever conducted by the Defense Department, and it won the award because its bid was "more advantageous" in four of the five key areas weighed in the contest.